Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to the prior art by inclusion in this section.
Standard Passive Entry Systems (PES) key fobs typically operate on two radio frequencies (RF). For example, low frequency (LF) communication is used for proximity detection and localization required for the Comfort Entry Go (CEG) functionality. Another frequency, such as ultra-high frequency (UHF), is used to extend the communication range for Remote Keyless Entry (RKE) functionality. Passive Entry Systems (PES) have strict proximity/localization requirements. For example, with a PES system providing RKE and CEG, a vehicle unlocks the doors only when a driver or a person authorized to access is within a perimeter at ˜2 m from the vehicle. The PES/CEG system further allows the user or the driver to start the engine only when the key fob is inside the vehicle. These localization requirements are hard to satisfy for any one wireless technology. Therefore, the current systems require LF, e.g. 125 kHz, antennas both inside and outside the vehicle along with optimal power control to satisfy the proximity/localization requirements. On the other hand, communication link from the key fob to the vehicle for RKE (i.e., when the user explicitly presses the lock/unlock button on the key fob) is based on UHF to satisfy both the range requirement (˜50 m) and the antenna size requirement (i.e., the antenna needs to fit in a small key fob).